1. Field of Invention
The present invention relates to a bonding pad structure on a semiconductor chip. More particularly, the present invention relates to a package-free bonding pad structure.
2. Description of Related Art
After years of development, semiconductor devices are now used almost everywhere. However, integrated circuit (IC) chips fabricated in a semiconductor manufacturing plant are practically useless unless they are properly packaged. The IC chip must first be mounted on a suitable carrier, and then the carrier itself must be enclosed by a protective casing before the IC chip can be inserted inside electrical equipment. In general, the packaging process can be roughly divided into three stages:
1. A proper carrier must be selected for holding the silicon chip. Different types of carriers are available including lead frames, film carriers and printed circuit boards (PCB). Normally, the use of a film carrier requires tape automatic bonding (TAB). PA1 2. The silicon chip must be electrically connected to the carrier. At present, the techniques for connecting a silicon chip to a carrier includes wire bonding, tape automatic bonding and flip chip or controlled collapse chip connection. PA1 3. The silicon chip and the carrier including their junction areas must be enclosed by epoxy resin, ceramics or other packaging material, thereby forming a rigid body for protecting the IC chip and its connecting elements.
However, before the contact points on an IC chip can be used to couple electrically with the carrier, a special structure for electrical connection such as a bonding pad or a bump must first be created at those contact points. Moreover, the establishment of a proper electrical connection between the bonding pads or bumps on the silicon chip with the carrier must be carried out in special processing stations. FIG. 1 is a schematic cross-sectional side view showing conventional wire connection between a bonding pad on a silicon chip and a lead frame pin using wire-bonding techniques. First, a metallic bonding pad 12 is formed on a silicon chip 10. Thereafter, the silicon chip and its surrounding lead frame are placed inside a specified wire-bonding machine. Next, the wire-bonding machine operates to bond one end of a short piece of conductive wire 14 to the bonding pad 12, and then followed by bonding the other end of the wire 14 to the lead frame pin 16. In general, the conductive wires 14 can be gold, aluminum or copper wires.
FIG. 2 is a schematic cross-sectional side view showing conventional electrical connection between a bonding pad on a silicon chip and tape carrier using tape automatic bonding techniques. The method includes forming a bump 20 either on top of a bonding pad 12 or on the inner lead 18 of a film carrier. Next, an inner lead bonding (ILB) operation is carried out to join the bonding pad 12 and a portion of the inner lead 18 together. Thereafter, an outer lead bonding (OLB) operation is carried out to join the outer lead with the electrode on a substrate plate using soldering, anisotropic conductive film (ACF) or photoharden insulation resin.
FIG. 3 is a schematic cross-sectional side view showing conventional electrical connection between a bonding pad on a silicon chip and a package medium using flip-chip techniques. Similarly, the flip-chip method involves the formation of a bump 22 on a bonding pad 12. A special machine must be used for aligning the bump 22 with the electrode 26 on a base substrate 26 and exerting a proper amount of pressure on the silicon chip. Finally, heating and underfilling operations have to be carried out by the machine.
However, in all three illustrations above, special processing operations using special processing stations have to be carried out just to link up with the bonding pads. Hence, additional processing time and production cost is incurred.